1. Field of the Invention
The present invention relates to optical fiber cables and structural members for optical fiber cables. More particularly, this invention relates to optical fiber cable structural members formed from composite materials containing thermotropic liquid crystalline polymer reinforcements which are formed in-situ with a matrix.
2. Description of the Prior Art
Optical fiber cables have been in use in the communications industry for a number of years to transmit information at very high rates over long distances. In an optical fiber cable the information is carried in the form of light signals through glass fibers with diameters on the order of 100 μm. These fibers are protected from the environment and external stresses by cable structures in which they are housed.
In designing optical fiber cable structures, it is important to ensure that stresses associated with cable installation and operational environment do not interfere with optical fiber performance. Generally, reinforcing materials are incorporated into cable structure designs in order to prevent the fibers from becoming strained by installation stresses or by mechanical or thermal stresses experienced during operation. Typical reinforcing materials utilized in cables have a high modulus and a low coefficient of thermal expansion (CTE). Reinforcing materials of choice have included steel, glass fibers or yarns, glass reinforced composites, polyester yarns, and aramid fibers or yarns. Aramid fibers or yarns are commonly used as reinforcing materials because they offer the best combination of mechanical properties and weight, but these materials are also characterized by a high cost. Aramid fibers and yarns are produced using polymers which are classified as liquid crystalline polymers (LCP). Liquid crystalline polymers are characterized by the ease in which molecular orientation occurs during melt or solution processing, resulting in the ability to obtain good mechanical properties in the process or machine direction. However, due to very high melting points of the polymeric materials used, conventional melt processing of aramid LCPs is not possible. Special processing equipment and technology must be used to produce aramid yarns containing LCP. This special processing equipment cannot be practically incorporated into an optical fiber cable manufacturing process. As a result, aramid yarns are produced separately and then incorporated into a cable structure as part of an additional manufacturing step. The addition of components or processing steps adds to the manufacturing costs and to the complexity of the production procedure.